pos-tags viterbi sequence-prediction scikit-learn syntactic-dependencies conditional-random-fields SyntaxNet NLTK NER word2vec tokenization tf-idf stanford-NER relationship-extraction named-entity-recognition naive-bayes multi-label-classification maximum-entropy-markov-models logistic-regression information-extraction hyperparameter-optimization hidden-markov-models grid-search gensim evaluation_metrics document-classification doc2vec dependency-graph PyData